38 TWINING PLANTS. Cuap. I. 
they were enabled to twine round trunks of trees, for 
they could not grow tall enough in a single season to 
reach the summit and gain the light. 
By what means certain twining plants are adapted to 
ascend only thin stems, whilst others can twine round 
thicker ones, I do not know. It appeared to me 
probable that twining plants with very long revolving 
shoots would be able to ascend thick supports ; accord- 
ingly I placed Ceropegia Gardnerti near a post 6 
inches in diameter, but the shoots entirely failed to 
wind round it; their great length and power of move- 
ment merely aid them in finding a distant stem 
round which to twine. The Spherostemma marmora- 
tum is a vigorous tropical twiner; and as it is a very 
slow revolver, I thought that this latter circumstance 
might help it in ascending a thick support ; but though 
it was able to wind round a 6-inch post, it could do 
this only on the same level or plane, and did not 
form a spire and thus ascend. 
As ferns differ so much in structure from phanero- 
gamic plants, it may be worth while here to show that 
twining ferns do not differ in their habits from other 
twining plants. In Lygodium articulatum the two 
internodes of the stem (properly the rachis) which 
are first formed above the root-stock do not move; 
the third from the ground revolves, but at first very 
slowly. This species is a slow revolver: but L. 
scandens made five revolutions, each at the average 
rate of 5hrs. 45 m.; and this represents fairly well the 
usual rate, taking quick and slow movers, amongst 
